Techniques for welding thermoplastic tubes

ABSTRACT

Thermoplastic tubes are welded together in a dry condition with the tubes being open and maintained in their undistorted condition during the welding step. In an alternative technique a branch tube is welded to a main tube by placing the tubes in a non-parallel orientation in a holding device. A wafer cuts completely through one tube to form two tube sections. The wafer also cuts a notch from the other tube. One of the tube sections is shifted to become aligned with the notched other tube and welded thereto. A further technique includes placing at least one tube in a holding device which has a false floor for pressing against an area of the tube while the tube is being flattened at two spaced locations on opposite sides of the area. When the false floor is moved away from the tube a partial vacuum results. An air pocket is formed when the tube is severed by a wafer by air flowing into the cut tube.

BACKGROUND OF INVENTION

This invention relates to improvements in the welding of thermoplastictubes. Various techniques are known for such welding operations.Copending application Ser. No. 51,390, filed May 18, 1987, the detailsof which are incorporated herein by reference thereto, discusses priortechniques as well as the particular techniques which are the subject ofthat invention. A common use of such techniques is in dialysis when itis necessary to provide a patient with a fresh supply of liquiddialysate. Under such circumstances the tube containing the olddialysate which leads from the patient to the supply is severed. Thesame apparatus severs a tube leading from the new supply. Theconventional techniques involve realigning the cut tubes so that thetube section from the new supply becomes aligned with the tube sectionfrom the patient. These aligned tube sections are then welded togetherto provide the patient with fresh dialysate.

The main emphasis in the techniques used heretofore have been concernedwith the welding of fluid-filled tubes. With such techniques means hadto be provided to flatten or seal each tube at two spaced locations sothat a cutting device, usually a heated wafer, may cut through the tubebetween the two spaced locations.

The conventional approaches taken heretofore have also been generallyconfined to cutting through parallel tubes and then realigning the tubeso as to form a single welded tube. Under certain circumstances,however, it would be desirable if the techniques could be utilized forwelding a branch tube to a main tube.

It would also be desirable if techniques could be provided which arecapable of welding fluid filled tubes wherein the cutting and weldingsteps take place in a portion of the tubes where there is no fluid.

SUMMARY OF INVENTION

An object of this invention is to provide a method of weldingthermoplastic tubes which are severed and welded while in their dryundistorted condition.

A further object of this invention is to provide a device and method ofwelding a branch tube to a main tube.

A still further object of this invention is to provide a device andmethod for welding round tubes containing fluid wherein the severing andwelding steps take place at a location having an air pocket.

In accordance with one aspect of this invention a pair of dry roundtubes are mounted in a holding device and are maintained in their dryround condition while the welding step takes place. In one embodiment ofthis invention, the tubes are mounted in a parallel relation during thesevering step and then realigned for the welding step. In an alternativeembodiment the tubes are pre-cut and then aligned to eliminate the needfor a shifting or realignment step.

A further aspect of this invention involves the welding of a branch tubeto a main tube. This is accomplished in a device wherein two tubes aremounted in non-parallel relation with a cutting device, preferably aheated wafer, moving relative to the tubes so as to completely cutthrough one tube and form two sections and to cut a notch from the othertube. The wafer is preferably non-linear so that non-linear cuts resultof complementary shape. The cut tubes are shifted to align one tubesection with the complementary shaped notched other tube and thesealigned tubes are welded together so that the tube section forms abranch of the other tube.

In yet another practice of this invention the tubes are mounted in aholding device wherein at least one of the holding devices includes twospaced pairs of clamping jaws with a gap therebetween for sealing thetube at two spaced locations. One of the pairs of clamping jaws includesa false floor for pressing against an area of the tube in a compressionzone between the spaced locations and forming a partial vacuum in thecompression zone. The movement of the false floor away from the tubecreates an air pocket at the gap so that a cutting device may cutthrough the tube at the air pocket.

THE DRAWINGS

FIGS. 1-7 are plan views schematically illustrating the sequence ofsteps in accordance with one practice of this invention;

FIGS. 8-11 are plan views schematically illustrating the sequence ofsteps in accordance with a further practice of this invention;

FIGS. 12 is a plan view schematically illustrating the first in asequence of steps in accordance with yet another practice of thisinvention;

FIG. 13 is a side elevation view showing a further step in accordancewith the practice of FIG. 12;

FIGS. 14-15 are plan views of yet further steps in accordance with thepractice of FIGS. 12-13;

FIG. 16 is an elevation view partly in section illustrating thecorrection of a branch tube to a main tube which results from thepractice of the invention illustrated in FIGS. 12-15;

FIG. 17 is a perspective view illustrating the device used in thepractice of the invention illustrated in FIGS. 12-15; and

FIGS. 18-21 are elevation views schematically illustrating the sequenceof steps in yet still another practice of this invention.

DETAILED DESCRIPTION

FIGS. 1-7 illustrate a practice of this invention which is remarkablysimpler than the conventional practice dealing with the welding of fluidfilled tubes since the practice of FIGS. 1-7 is directed to dry tubes.As previously indicated the prior art has concentrated its efforts onthe welding of fluid filled thermoplastic tubes such as used indialysis. There are, however, many circumstances ignored by the priorart where it is desirable to weld thermoplastic tubes which do notcontain fluid, but rather are in a dry condition. Such circumstancescould include laboratory or test work as well as hospital pharmacyroutines or methods wherein fluid is supplied only periodically. FIGS.1-7 schematically illustrate the principles upon which this aspect ofthe invention is based. It is to be understood that once given theteachings of this invention those skilled in the art could use anysuitable equipment for carrying out the invention. Copending applicationSer. No. 51,390 filed May 18, 1987 for example describes suitableequipment which could be modified to eliminate the clamping steps andotherwise be used in the practice of this invention. Accordingly, thedetails of that application are incorporated herein by referencethereto, rather than describing those details except as is necessaryherein for an understanding of this invention.

As shown in FIG. 1 a pair of tubes 10, 12 made of thermoplastic materialsuch as conventionally known in the prior art is mounted in parallelrelation in a holding device 14 which includes a first clamp unit 16 anda second clamp unit 18 spaced from each other to form a gap 20. Althoughunits 16 and 18 are referred to as clamp units, the only clamping thatis necessary is to hold the tubes in place without flattening the tubeswhich differs from the prior art approach. During this loading stepwafers 22, 24 are heated to their intended temperatures. Wafer 22 is acutting wafer and is heated for example to 350° F. Wafer 22 ispreferably provided with a non-stick surface. Wafer 24 is made forexample of nichrome and is heated to a temperature between 500°-1200° F.since it functions in the welding step. Such wafers are known in theart.

FIG. 2 illustrates the severing step in which there is relative movementbetween the holding device 14 and wafer 22 so that warm wafer 22 passesinto gap 20 to cut through tubes 10, 12.

FIG. 3 shows the sequence of operation wherein clamping unit 16 is movedaway from clamping unit 18.

FIG. 4 illustrates the realigning step wherein clamping unit 16 isshifted as indicated so that a tube section from tube 10 in clampingunit 16 becomes aligned with a tube section from clamping unit 18. Inthis step warm wafer 22 is no longer between the cut tubes; rather hotwafer 24 is located between the aligned tube sections.

FIG. 5 illustrates the step wherein there is a pause to allow radiantheat from hot wafer 24 to melt and simultaneously sterilize the alignedtube ends.

FIG. 6 illustrates the step wherein hot wafer 22 is moved away from thealigned tube ends.

FIG. 7 illustrates the final sequence wherein clamping unit 18 isshifted to push the heated aligned tube ends together and effect theweld.

The advantages of the method of FIGS. 1-7 is that it provides asimplified technique for joining round dry tubes.

FIGS. 8-11 show a variation of the method of FIGS. 1-7. As indicatedtherein tube 26 and tube 28 are pre-cut so that their tube ends arereasonably squared. FIG. 8 illustrates the initial step where thepre-cut tubes 26, 28 are mounted in a pair of clamping units 30, 32similar to units 16, 18 except that units 30, 32 need accommodate onlyone tube rather than a pair of tubes. As shown in FIG. 8 tube ends 26,28 are pressed against a cold wafer 34.

FIG. 9 illustrates the next step of operation wherein the wafer 34 isturned on or heated and the tube ends 26, 28 are pressed into contactwith wafer 34 by the shifting of clamping units 30, 32. During this stepthe surface of the tube ends is flattened to assure proper contactduring the later welding step. The presence of the non-heated tubesholds down the wafer temperature. The wafer itself could be providedwith a built-in temperature control.

FIG. 10 illustrates the next step wherein clamping units 30, 32 aremoved away from each other to pull the tubes out of contact with andaway from wafer 34. This allows the wafer temperature to rise andradiantly melt the exposed tube ends.

FIG. 11 shows the next step wherein wafer 34 is moved away from the tubeends. Clamping units 30, 32 are then moved toward each other to pressthe tube together and make the weld.

The practice of FIGS. 8-11 thus includes all of the advantages of thepractice of FIGS. 1-7 but is even more simplified because it eliminatesthe shifting step.

FIGS. 12-17 relate to the practice of this invention wherein a branchtube is connected to a main tube. The device for practicing thisembodiment of the invention is best illustrated in FIG. 17. It is notedthat this practice may be used with fluid filled tubes.

As shown in FIG. 17 branch welding device 36 includes a holding devicewhich comprises a first pair of clamping units 38 and a second pair ofclamping units 40. Clamping units 38 clamps a first tube 42 in aparticular orientation while clamping unit 40 clamps a second tube 44 ina non-parallel orientation. For example, as illustrated one of the tubes42 is horizontal while the other tube 44 is vertical or perpendicularthereto. It is to be understood however that any suitable non-parallelrelationship may be used within the practice of this invention. Eachclamping unit comprises two sets of clamping jaws. Clamping unit 38includes for example a set of clamping jaws 46, 48 and a second set ofspaced clamping jaws 50, 52 so as to press against and clamp tube 42.Clamping unit 40 includes a pair of clamping jaws 54, 56 which cooperatewith clamping jaws 50, 52 to clamp tube 44. The various clamping jawsare spaced from each other to provides gaps which jointly form anunobstructed path 58 into which the tubes 42 and 44 extend.

In the preferred practice of this invention the cutting and heating isaccomplished by a wafer 60 which is bent so as to be non-linear. Wafer60 is positioned for relative movement in path 58 by either maintainingthe wafer stationery and moving holding device 36 or, as illustrated, bymounting wafer 60 on any suitable support 62 which would beappropriately positioned so that it could move wafer 60 through path 58without support 62 contacting the tubes.

FIG. 12 shows the step wherein tubes 42, 44 are mounted in the clampingunits 36, 40 and flattened by moving clamping jaws 46, 48 and jaws 54,56 toward stationary jaws or anvils 50, 52 as indicated by the arrows.

After the flattening step of FIG. 12 the severing step of FIG. 13 takesplace. As illustrated wafer 60 cuts completely through tube 42 to form apair of tube sections 42a, 42b. Because wafer 60 is non-linear the tubesections likewise have non-linear ends. As wafer 60 continues to movethrough path 58 wafer 60 cuts a notch from tube 44 with the notch havinga shape complementary to the non-linear end of tube end 42b such as aV-shape. The severed material 44a (FIGS. 14-15) would have a shapecomplementary to tube end 42a. As illustrated, path 58 has a shapeconforming to the shape of wafer 60.

FIG. 14 illustrated the next step of operation wherein wafer 60 isremoved from path 58 and the clamping jaws are moved toward therealigning position that is illustrated in FIG. 15. In this realigningposition tube end 42b fits into the notch in tube 44. Tube end 42comprises a stub end which is sealed because of its flattened condition.Several material 44a will later be discarded. The aligned tube end 42band tube 44 are then pressed together as shown in FIG. 15 to effect thewelding operation in the known manner.

FIG. 16 illustrates the resulting tube structure wherein tube 44comprises a main tube and tube end 42b is the branch tube.

The embodiment of FIGS. 12-17 has a number of advantages. For example,the tubes 42, 44 need not be of the same diameter to be joined together.Additionally, the branch tube could be connected to the main tube at anyangle and need not be perpendicular thereto.

FIGS. 18-21 illustrate yet a further practice. The device 64 is utilizedfor forming an air pocket in the tube being cut so that the wafer maycut through the air pocket in the otherwise fluid filled tube. FIGS.18-21 illustrate the practice of this invention involving the cutting ofa single tube. The invention may be practiced wherein the same conceptof air pocket cutting may be used for both tubes to be welded togetheror wherein an air pocket is formed in only one of the pair of tubes.

As shown in FIG. 18 tube 66 is loaded or installed in spaced holdingdevices 68, 69 having a gap therebetween. Each holding device comprisesa set of clamping jaws. One set of clamping jaws includes a lower jaw 70having a clamping edge 72. Jaw 70 is associated with upper jaw 74 havinga clamping edge 76. The second set of clamping jaws includes a lower jaw78 having a clamping edge 80. The central portion of clamping jaw 78includes a passageway which is plugged by a false floor 82 in the formof a slidable block having its upper surface generally coplanar with theupper surface of jaw 78 as illustrated. Upper clamping jaw 84 has a flatlower surface 86 along the major part of its length so that a corner ofclamping jaw 84 is located in line with clamping edge 80. A trigger 88or movable stop is located below false floor 82 to maintain false floor82 in the position shown in FIG. 18.

When upper clamping jaws 74 and 84 are moved downwardly toward the lowerclamping jaws tube 66 is sealed or flattened at two spaced locations 90,92. An area of tube 66 is also compressed where clamping jaw 84 pressesthe tube 66 against false floor 82. This area is referred to as acompression zone 94. The portions of tube 66 outwardly of sealed points90, 92 is under normal pressure. In the condition shown in FIG. 19 tube66 is filled with fluid throughout the region between sealed points 90,92.

FIG. 20 shows the next step of operation wherein trigger 88 is shiftedout of contact with false floor 82. As a result floor 82 drops in thepassageway of clamping jaw 78 so that tube 66 is no longer undercompression in the compression zone. As a result tube 66 tends to expandtoward its original diameter which creates a partial vacuum incompression zone 94. At the same time the wafer holder is beginning tomove wafer 96 into the gap 98 between the clamping units 64, 68.

Hot wafer 96 is then moved through gap 98 to cut through tube 66. Thesevering of tube 66 by the hot wafer 96 creates an air pocket 100 to beformed caused by air being sucked into the tube 66 as indicated by thearrows 102. The fluid remains in tube 66 without flowing into the airpocket 100 because for example of surface tension with a miniscus beingformed at each of the cut ends of tube 66.

The practice of this invention is particularly intended to be used withsmall diameter tubes such as 3/8" or less so that the air pocket 100will be maintained without fluid flowing into the air pocket. It is alsoto be understood that although FIG. 21 illustrates the cutting operationto take place by using a vertically moving wafer 96, the invention maybe practiced with a horizontally moving wafer.

The embodiment of FIGS. 18-21 is particularly advantageous because itutilizes the partial vacuum effect to cause fluid to jump away from theinitial cut tube and permit an air pocket to result. Although the cuttube is essentially filled with fluid the presence of the air pocket andthe negative pressure products the operator from the contents of thefluid. This practice is also advantageous because it is a simpleoperation which is transparent to the operator.

After a pair of tubes have been cut, using the concepts of FIGS. 18-21for at least one tube, the cut tubes are shifted into realignment andwelded as previously described.

We claim:
 1. A device for forming a branch connection of a thermoplastictube to the side wall of a second thermoplastic tube comprising aholding device, said holding device comprising a first pair of clampingunits for clamping a first tube extending across said clamping units,said clamping units being spaced from each other to provide anunobstructed path therebetween, a second pair of clamping units forclamping a second tube in an orientation non-parallel to the first tube,said second pair of clamping units being spaced from each other andhaving an unobstructed path in line with and communicating with saidunobstructed path of said first pair of clamping units whereby thesecond tube may extend across said unobstructed path, cutting meansrelatively movable in said unobstructed path for cutting through thefirst tube to create a pair of tube sections and for cutting a notchfrom the second tube, one of said first pair of clamping units and oneof said second pair of clamping units on the same side of saidunobstructed path being shiftably mounted to realign the cut tubes foraligning one of the tube sections with the second tube at the locationof the cut notch, means for heating the notch of the realigned secondtube and the cut end of the tube section realigned with the notch, andmeans for pressing the heated realigned cut tubes to weld the cut tubestogether whereby the welded tube section forms a branch to the secondtube.
 2. The device of claim 1 wherein said cutting means comprises abent wafer to form non-linear complementary cuts.
 3. The device of claim2 wherein said wafer is heated to comprise said heating means.
 4. Thedevice of claim 3 wherein said unobstructed path has a shape conformingto the shape of said bent wafer.
 5. The device of claim 4 wherein saidfirst pair of clamping units comprises a first pair of spaced clampingjaws with a portion of said unobstructed path therebetween, a pair ofspaced anvils associated with first pair of clamping jaws for insertingthe first tube between said first pair of clamping jaws and said pair ofanvils, a portion of said unobstructed path being the spacing betweensaid anvils, said second pair of clamping units comprising a second pairof clamping jaws with a portion of said unobstructed path therebetween,and said second pair of clamping jaws being associated with said pair ofanvils for inserting the second tube between said second pair ofclamping jaws and said pair of anvils.
 6. The device of claim 5 whereinsaid first pair of clamping jaws and said second pair of clamping jawsare movable toward said anvils to flatten the first and second tubes. 7.The device of claim 6 wherein one of said first pair of clamping jawsand one of said anvils and one of said second pair of clamping jaws onthe same side of said unobstructed path are laterally shiftable withrespect to said clamping jaws and said anvil on the other side of saidpath to effect the realignment of the tubes.
 8. The device of claim 7wherein said second pair of clamping jaws holds the second tube in anorientation perpendicular to the first tube.
 9. The device of claim 2wherein said wafer has a V-shape.
 10. The device of claim 2 wherein saidwafer is mounted on a mount for movement into and out of saidunobstructed path.
 11. The device of claim 2 wherein said wafer isstationarily mounted and said unobstructed path is movable with respectto said wafer.
 12. A method for forming a branch connection from a firstthermoplastic tube to the side wall of a second thermoplastic tubecomprising mounting the first tube across a gap between a first pairclamping units, mounting a second tube in a second pair of spacedclamping units with a spacing between the second pair of clamping unitsbeing in line with the gap and forming a continuous unobstructed pathand with the second tube being in an orientation non-parallel to thefirst tube and with the second tube extending across the unobstructedpath, moving a cutting device through the unobstructed path to cut thefirst tube into a pair of cut sections and to cut a notch from thesecond tube, realigning the tubes to align one of the cut sections withthe notched second tube, heating the notch of the realigned second tubeand the cut end of the tube section realigned with the notch, andpressing the heated realigned tubes to weld the cut section to thenotched second tube whereby the cut section forms a branch of the secondtube.
 13. The method of claim 12 wherein the cutting device is a bentheated wafer which cuts and heats the tubes.
 14. The method of claim 12wherein the second tube is perpendicular to the first tube.
 15. Themethod of claim 12 wherein the first tube has a different diameter thanthe second tube.
 16. The method of claim 12 wherein the tubes areflattened before being cut.